jonathan karl, abc news, washington. >> we bring in abc's medical editor dr. richard besser. exactly what does a stent do and what does it not do? >> this tiny little thing here is a stent. what it does do, if you have symptoms it can relieve those. what it doesn't do, if you don't have heart symptoms, it doesn't prevent a heart attack. >> it does not prevent a heart attack? we think of it as opening it up so the plaque doesn't cause a heart attack but that's wrong. >> that's right. many studies have shown if you don't have symptoms it doesn't do anything for you. if you have shortness of breath, chest pain, fatigue going upstairs or strange symptoms, that's when you need to ask about getting a stress test to see if your arteries might be blocked. >> we'll be following the former president tomorrow hoping he's home. thank you again. >>> and now we turn to that shooting rampage trial under way at fort hood texas and the opening statement by army major nadal hassan who is defending himself. the former psychiatrist admitted killing 13 people and wounded dozens of others. hassan,